The extracellular concentrations of the lipid peroxidation product mal
onaldehyde (MDA) and the antioxidants ascorbic and uric acid were meas
ured in rat brain in vivo using microdialysis coupled to HPLC with ult
ra violet spectrophotometry. Treatment with kainic acid at pH 4.1 (50
nmol) caused a significant increase in the sampled concentration of MD
A but no significant changes in the antioxidants. Treatment with the s
ame dose of kainic acid at pH 7.2 did not cause a significant increase
in MDA, although some changes were noted in the antioxidants. The pap
er demonstrates the ability to monitor changes of a lipid peroxidation
breakdown product as a measure of oxidative stress in vivo. Furthermo
re, the data suggests that the toxic action of kainic acid in acute pr
eparations may be due to the elevation of hydrogen ions.